There are many known welding processes, used in many different applications. Two well known welding applications are controlled short circuit welding and pulse welding.
Controlled short circuit welding includes waveform controlled short circuit welding and mechanically controlled short circuit welding. Waveform controlled short circuit welding controls the process by controlling the output voltage and current (the power waveform) to have desired values, such as that which will reduce spatter by reducing the pinch force (current) when the liquid-metal bridge of the short is about to break and establish an arc. Mechanically controlled short circuit welding controls the process by controlling the breaking of the short by retracting the wire (mechanically controlling the wire and process) and can reduce the current and/or voltage to a desired level before the wire is retracted.
Known waveform controlled short circuit welders often have a converter or inverter controlled to provide the desired output. Generally, they lower the current prior to the short clearing so that the current is low when the short clears and the arc forms. The current is lowered because the clearing can be an explosive event, and lower current reduces spatter. Such systems attempt to sense or predict the short ending, and lower the current in response thereto. For example, U.S. Pat. Nos. 6,087,626 and 6,326,591 to the present inventors (hereby incorporated by reference), describe a topology and control that are used for short arc welding. They predict the short clearing, and reduce the inverter output before the short clears.
Other waveform controlled short circuit welders include an output bypass switch that shunts a resistance between the power circuitry and the weld. This switch is used to lower the current faster than commanding the inverter (or other power circuit) can lower the current. An example of such a system is found in U.S. Pat. No. 5,001,326 (hereby incorporated by reference), as well as in a number of related patents. Switch 70 of that patent is referred to herein as an output bypass switch because it is on the output of the inverter, and allows the output current to be more quickly reduced than it would be by control of the power circuitry alone. Power circuits used with this sort of system include inverters and dc supplies.
Pulse welding generally consists of the output current alternating between a background current and a higher peak current. Most of the transfer (of the wire to the weld) occurs during the peak state. Pulse MIG welding systems are also well known. They have variety of power topologies, and differ from some waveform controlled short circuit power supplies by having a lesser output inductance, and not having the output bypass switch. They also have a control scheme that provides the pulse power, rather than controlled short circuit power.
Many prior art welding power supplies have either been used for waveform controlled short circuit welding or for pulse (MIG) welding, and have had their power topology and control scheme optimized for the single process. More recently, multi-process welding-type power supplies have become known. Controlled short circuit welding is particularly well suited for performing a root pass on a pipe and pulse (MIG) welding is particularly well suited for performing fill passes on a pipe. Thus multi process waveform controlled short circuit and pulse power supplies may be well suited to pipe welding
However, welding-type power supplies that provide waveform controlled short circuit welding power and pulse welding power have two torch output studs—one for the waveform controlled short circuit output and one for the pulse output (and one workpiece stud for the return current path). Thus, after completing the root pass the user must switch weld cables (if two torch cables are present), or move the cable from the controlled short circuit stud to the pulse stud. This is wasteful and/or time consuming.
Accordingly, a multi process controlled short circuit and pulse welding power supply with a single torch output stud that provides both controlled short circuit and a pulse output is desirable.